This application claims priority to Japanese Patent Application NO. P2001-370613 filed on Dec. 4, 2001, the contents of which are hereby incorporated by reference.
The present invention relates to a spatial light modulator for spatially modulating incident light by utilizing a magneto-optic effect.
A spatial light modulator for spatially modulating incident light is used in the field of optical information processing, computer-generated holograms or the like.
Conventional spatial light modulators include one in which a liquid crystal is used and one in which a micro-mirror device is used.
In the above-mentioned field of optical information processing, computer-generated holograms or the like, it is necessary that a large amount of information be processed at high speed, and therefore it is desirable that the spatial light modulator should have a high operation speed.
However, the spatial light modulator in which a liquid crystal is used has a low operation speed. For example, even in the case of using a ferroelectric liquid crystal that has a high operation speed among liquid crystals, the response time is on the order of microsecond.
The spatial light modulator in which a micro-mirror device is used can operate at a relatively high speed. However, the manufacturing cost for this spatial light modulator is high because it is a micro machine having a complicated structure which is manufactured by a highly-developed semiconductor manufacturing process. Moreover, there remains a problem in reliability because it has a mechanical driving portion.
For example, U.S. Pat. Nos. 4,584,237, 5,241,421, 5,255,119 and 5,386,313 disclose spatial light modulators for modulating incident light by utilizing a magneto-optic effect. Hereinafter, such a spatial light modulator is referred to as a magneto-optic spatial light modulator. The magneto-optic spatial light modulator includes a plurality of pixels, each of which is made of a magneto-optic material and capable of selecting a direction of magnetization independently. In the magneto-optic spatial light modulator, a direction of polarization of light passing through each pixel is rotated by a predetermined angle in a direction opposite to the direction of magnetization of the pixel due to the Faraday effect. Accordingly, the magneto-optic spatial light modulator produces spatially modulated light by arbitrarily selecting a direction of magnetization for each pixel.
Since the magneto-optic spatial light modulator exhibits a high speed in reversing the direction of magnetization of each pixel, it can achieve a higher operation speed on a pixel-by-pixel basis than that of a spatial light modulator in which a liquid crystal is used.
A conventional magneto-optic spatial light modulator emits two types of light which are different in direction of polarization. The two types of light, when passed through an analyzer, become two types of light having different light intensities. The two types of light having different light intensities are distinguishable from each other by comparing the intensities with a predetermined threshold value. There is a problem, however, in that the distinction method is susceptible to noise.
On the other hand, a technique is known in which 1-bit digital data xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d are expressed using two adjoining pixels of the spatial light modulator, and the data are distinguished by differentially detecting a difference in light intensity between two beams of light from the two adjoining pixels. However, since a single bit digital data is expressed using two pixels, the technique suffers from a problem that the amount of information producible by the spatial light modulator decreases to half that of the case where a single bit digital data is expressed using a single pixel.
It is an object of the invention to provide a spatial light modulator for spatially modulating incident light by utilizing a magneto-optic effect, capable of generating spatially modulated light that is highly resistant to noise, without reducing the amount of information producible.
A spatial light modulator of the invention comprises:
a magnetic layer made of a magneto-optic material and including a plurality of pixels whose directions of magnetization are set independently of one another, each of the pixels causing rotation of a direction of polarization of incident light depending on its direction of magnetization due to a magneto-optic effect;
a plurality of soft magnetic layers located near the respective pixels, each of the soft magnetic layers being selectively magnetized in either of two opposite directions depending on a magnetic field from exterior; and
a magnetic field generator for generating a magnetic field for setting the direction of magnetization of each of the soft magnetic layers, wherein
each of the pixels includes two regions that take different states of magnetization when the soft magnetic layer nearby is magnetized, directions of magnetization in the two regions changing depending on the direction of magnetization of the soft magnetic layer.
According to the spatial light modulator of the invention, directions of magnetization of the soft magnetic layers are set by magnetic fields generated by the magnetic field generator. The two regions of each pixel take different states of magnetization when the soft magnetic layer near the pixel is magnetized. The directions of magnetization in the two regions change depending on the direction of magnetization in the soft magnetic layer. As a result, each pixel generates two types of light selectively.
In the spatial light modulator of the invention, the magnetic field generator may include a plurality of first conductor layers and a plurality of second conductor layers arranged to intersect each other at positions corresponding to the pixels, currents for generating the magnetic field for setting the direction of magnetization of each of the soft magnetic layers being passed through the first and second conductor layers.
The spatial light modulator of the invention may further comprise a bias field applying device that applies to the magnetic layer a bias magnetic field used for changing the direction of magnetization of each of the pixels.
Other objects, features and advantages of the invention will become sufficiently clear from the following description.